Sulfur dioxide-cured epoxy acrylate foundry binder system

ABSTRACT

The present invention provides an epoxy acrylate foundry binder composition having an epoxy resin component (Part 1) and an acrylate component (Part 2) containing about 1% to less than about 6% by weight of a borate ester. The epoxy acrylate binders of the present invention are useful in making foundry cores and molds in that the addition of the borate ester increases hot strength of the binder system. Also provided is a cold-box process for making sand cores and molds using the epoxy acrylate binders cured by sulfur dioxide vapor.

FIELD OF THE INVENTION

The present invention relates to improved epoxy acrylate foundry bindercompositions having an epoxy resin component and an acrylate componentuseful in making sulfur dioxide (SO₂)-cured foundry cores and molds.More particularly, this invention relates to the use of borate esterssuch as trialkyl borates in the acrylate component of such foundrybinder compositions to improve hot strength and thus preventerosion-related defects.

BACKGROUND OF THE INVENTION

An important process used in the foundry industry for making metal partsis sand casting. In sand casting, disposable foundry shapes, includingmolds and cores, are made by shaping and curing a foundry mix. Thefoundry mix is a mixture of an appropriate aggregate (typically sand)and an organic or inorganic binder. The function of a binder is to bondthe aggregate together to make molds and cores.

One foundry process that is commonly used for making cores and moldsentails the use of sulfur dioxide (SO₂) to cure the epoxy acrylatebinder system. This is a variant of the “cold-box” process in which amixture of a peroxide, an epoxy resin, a multifunctional acrylate, andoptional diluents and/or additives are mixed with an aggregate andcompacted into a pattern to give the mixture a specific shape. Theshaped mixture is contacted with SO₂ vapor (optionally diluted withnitrogen), by blowing the SO₂ into the pattern in which the shape iscontained so that the SO₂ reacts with the peroxide to form an acid andfree radicals. The acid cures the epoxy resin and the free radicals curethe multifunctional acrylate rapidly hardening the mixture to producethe core or mold which can be used immediately in a foundry core and/ormold assembly.

Although the binder composition can be added to the foundry aggregateseparately, it is preferable to package the epoxy resin and free radicalinitiator (peroxide) as a “Part 1” and add this package to the foundryaggregate first. The ethylenically unsaturated material (acrylate) isthen preferably added to the foundry aggregate as the “Part 2,” eitheralone or along with some of the epoxy resin before curing with SO₂vapor.

Although SO₂-curing has been used successfully in many foundries, one ofthe weaknesses of SO₂-cured epoxy acrylate binder systems has been thelack of adequate erosion resistance. Erosion occurs when molten hightemperature metals (such as iron or steel) contact the mold or coresurfaces during the pouring process and sand is dislodged at the pointof contact. Such erosion occurs because the binder does not havesufficient heat resistance, or “hot strength,” to maintain surfaceintegrity until the pouring process is complete. The resulting loosesand may be carried into the mold cavity by the liquid metal, creatingsand inclusions and weak areas in the casting. Dimensional defects mayalso be created on the surface of the casting caused by metalpenetration into the surface of the mold or core.

To correct this problem, foundries have historically resorted to the useof refractory coatings to increase hot strength thereby improvingresistance to defects caused by impingement of the high temperaturemetal on mold or core surfaces. For example, core and mold assemblies orparts thereof are coated with a slurry consisting of a high meltingrefractory oxide, a carrier, and thixotropic additives. Once dried onthe mold or core surface, the coating helps prevent erosion in mostcases. However, this approach is messy, adds complexity to the sandcasting process, and requires expensive gas-fired, microwave, or radiantenergy ovens to cure or set the coating making it cost prohibitive andinefficient. In addition, when the cores and/or molds are heated duringthe drying process, the strength of the organic binder-to-aggregate bondmay be significantly weakened sometimes making handling of the hot coresproblematic and reducing productivity due to distortion or cracking ofthe core or mold.

Thus, there is a need for an SO₂-cured epoxy acrylate binder system thatcan provide foundry shapes with adequate hot strength during the castingprocess. If a way could be found to make such a binder with increasedthermal stability, it would show increased hot strength properties suchas increased collapsibility time in a foundry core and would represent auseful contribution to the art. Additionally, because the improvedfoundry shapes would be more resistant to erosion, they could be used tocast metal articles without coating the foundry shapes with refractorymaterials.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, there is provided a sulfurdioxide-curable binder composition comprising an epoxy resin componentincluding at least one epoxy resin and a free radical initiator and anacrylate component including at least one acrylate and a boric acidester. The boric acid ester is present in the binder composition in anamount of about 1% to less than about 6% by weight based on the weightof the acrylate component. In a preferred embodiment, the boric acidester is a trialkyl borate. In a more preferred embodiment, the trialkylborate is tri(C₂-C₈)alkyl borate.

In another embodiment, there is provided a sulfur dioxide-curablefoundry mix comprising aggregate and a binder including an epoxy resincomponent (Part 1) and an acrylate component (Part 2). The epoxy resincomponent includes at least one epoxy resin and a free radicalinitiator, and the acrylate component includes at least one acrylate andabout 1% to less than about 6% by weight of a boric acid ester, based onthe weight of the acrylate component. The binder will be used at a levelof from about 0.5% to about 2% based on the total weight of the foundrymix. In a preferred embodiment, the boric acid ester is a trialkylborate. Preferred trialkyl borates include tri(C₂-C₈)alkyl borates. Aparticularly preferred trialkyl borate is tri-n-butyl borate.

In another embodiment, there is provided a cold-box method of making afoundry shape by preparing a foundry mix by admixing aggregate and abinder comprising an epoxy resin component including at least one epoxyresin and an effective amount of a peroxide and an acrylate componentincluding at least one acrylate and a boric acid ester. The boric acidester will be present in an amount of about 1% to less than about 6% byweight based on the weight of the acrylate component and the binder willbe present in an amount from about 0.5% to about 2% based on the totalweight of the foundry mix. The resulting foundry mix is shaped to adesired configuration to provide a shaped foundry mix. The resultingshaped foundry mix is cured with gaseous sulfur dioxide to provide afoundry shape for casting metal parts. In a preferred embodiment, theboric acid ester is a trialkyl borate. In a more preferred embodiment,the trialkyl borate is tri(C₂-C₈)alkyl borate.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, it has now been found thataddition of esters of boric acid (“borate esters”) such as trialkylborates to an epoxy acrylate binder composition provides unexpectedimprovements in hot strength properties in foundry cores and molds. Thefoundry binder system includes an epoxy resin component (Part 1) and anacrylate component (Part 2). The trialkyl borate is preferably added tothe acrylate component (Part 2) of the binder.

The term “alkyl,” as used herein, refers to a monovalent saturatedstraight or branched chain hydrocarbon, or a monovalent saturated cyclichydrocarbon, having the number of carbons designated (i.e. C₁-C₈ meansone to eight carbons). Examples include: methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl,neopentyl, n-hexyl, n-octyl, n-decyl, n-dodecyl and cyclohexyl.

The term “aryl,” as used herein, refers to a carbocyclic aromatic systemcontaining one or more rings (typically one, two or three rings) whereinsuch rings may be fused. The aromatic rings may be substituted with oneor more substituents, for example, alkyl. Examples include: phenyl,naphthyl, anthracyl, o-cresyl, m-cresyl and p-cresyl.

Trialkyl and triaryl borates are organic boron compounds that arederived from boric acid, specifically esters of boric acid (“borateesters”). Preferred trialkyl borates include tri(C₂-C₈)alkyl borates.Representative useful tri(C₂-C₈)alkyl borates are triethyl borate,tri-n-propyl borate, tri-isopropyl borate, tri-n-butyl borate,tri-isobutyl borate, tri-sec-butyl borate, tri-tert-butyl borate, andtri-n-octyl borate. A particularly preferred trialkyl borate istri-n-butyl borate (TBB). Useful triaryl borates include triphenylborate, tri-o-cresyl borate, tri-m-cresyl borate and tri-p-cresylborate. These and other suitable boric acid esters may be used inaccordance with the present invention.

The borate esters used in the present invention must be soluble in theacrylate component (Part 2).

Furthermore, the borate ester may be present in an amount from about 1%to less than about 6% by weight, based on the weight of the acrylatecomponent (Part 2). In a preferred embodiment, the borate ester ispresent in an amount from about 1% to about 5% by weight, based on theweight of the acrylate component. In a more preferred embodiment, theborate ester is present in an amount from about 2% to about 4% byweight, based on the weight of the acrylate component. In a particularlypreferred embodiment, the borate ester is a tri(C₂-C₈)alkyl borate.Higher use levels of certain higher carbon borate ester compounds (e.g.tri-n-octyl borate) may be required in certain applications, due to thecorresponding increase in molecular weight of these compounds.

The epoxy resin component (Part 1) contains at least one epoxy resin. Anepoxy resin is a resin having an epoxide group. Examples of epoxy resinsinclude (1) diglycidyl ethers of bisphenol A, B, F, G and H, (2) epoxynovolacs, which are glycidyl ethers of phenolic-aldehyde novolacs, and(3) mixtures thereof.

Epoxy resins (1) are made by reacting epichlorohydrin with the bisphenolcompound in the presence of an alkaline catalyst. By controlling theoperating conditions and varying the ratio of epichlorohydrin tobisphenol compound, products of different molecular weights can be made.Epoxy resins of the type described above based on various bisphenols areavailable from a wide variety of commercial sources.

Examples of epoxy novolac resins (2) include epoxy cresol and epoxyphenol novolacs produced by reacting a novolac resin (usually formed bythe reaction of ortho-cresol or phenol and formaldehyde) withepichlorohydrin, 4-chloro-1,2-epoxybutane, 5-bromo-1,2-epoxypentane,6-chloro-1,3-epoxyhexane, and the like. In addition, other epoxy resinsmade from phenolic resins such as phenolic resoles or resitols, may beused. One useful epoxy novolac is EPON™154 (Hexion Specialty Chemicals,Inc., Houston, Tex.).

Preferred levels of epoxy resins in the epoxy resin component (Part 1)of the present invention are: Bisphenol A epoxy: 0-50% by weight, basedon the weight of the epoxy resin component; Bisphenol F epoxy: 0-70% byweight, based on the weight of the epoxy resin component; and epoxynovolac: 0-25% by weight, based on the weight of the epoxy resincomponent.

Drying oils may be used in the epoxy resin component (Part 1). Usefuldrying oils are glycerides of fatty acids which contain two or moredouble bonds and can polymerize. Examples of some natural drying oilsinclude soybean oil, sunflower oil, hemp oil, linseed oil, tung oil,oiticica oil and fish oils, and dehydrated castor oil, as well as thevarious known modifications thereof (e.g., the heat bodied, air-blown,or oxygen-blown oils such as blown linseed oil and blown soybean oil).Also, esters of ethylenically unsaturated fatty acids such as tall oilesters of polyhydric alcohols such as glycerine or pentaerythritol ormonohydric alcohols such as methyl and ethyl alcohols can be employed asthe drying oil. One preferred ester is butyl ester of tall oil fattyacid. If desired, mixtures of drying oils can be employed.

The epoxy resin component (Part 1) must include a free radicalinitiator. Preferably, the free radical initiator is a peroxide and/orhydroperoxide. Further examples include ketone peroxides, peroxy esterfree radical initiators, alkyl oxides, chlorates, perchlorates, andperbenzoates. Hydroperoxides particularly preferred in the inventioninclude t-butyl hydroperoxide, cumene hydroperoxide, paramenthanehydroperoxide, and the like. The organic peroxides may be aromatic oralkyl peroxides. Examples of useful diacyl peroxides include benzoylperoxide, lauroyl peroxide and decanoyl peroxide. Examples of alkylperoxides include dicumyl peroxide and di-t-butyl peroxide.

The acrylate component (Part 2) contains at least one acrylic resin(“acrylate”). Acrylic resins include acrylate monomer, oligomer,polymer, or mixtures thereof, which contain ethylenically unsaturatedbonds. Examples of such materials include a variety of mono functional,difunctional, trifunctional, tetrafunctional and pentafunctionalmonomeric acrylates and methacrylates. A representative listing of thesemonomers includes alkyl acrylates, acrylated epoxy resins, cyanoalkylacrylates, alkyl methacrylates, cyanoalkyl methacrylates, anddifunctional monomeric acrylates. Other acrylates which can be usedinclude trimethylolpropane triacrylate, hexanediol diacrylate,pentaerythritol tetraacrylate, methacrylic acid and 2-ethylhexylmethacrylate, the first two compounds being particularly preferred.Typical reactive unsaturated acrylic polymers, which may also be usedinclude epoxy acrylate reaction products, polyester/urethane/acrylatereaction products, acrylated urethane oligomers, polyether acrylates,polyester acrylates, and acrylated epoxy resins. In addition, phenolicurethane resins or other phenolic resins can be combined with theacrylates in the Part 2 component. A useful phenolic urethane resin isSigma Cure 705 (HA International LLC, Westmont, Ill.). Also, optionallyan effective amount of an epoxy resin may be used in the Part 2component.

It will be apparent to those skilled in the art that other additivessuch as antioxidants, silanes, silicones, benchlife extenders, releaseagents, defoamers, wetting agents, etc. can be added to the aggregate orto the foundry mix. Useful antioxidants include butylated phenols andbutylated cresols. Useful silanes include, but are not limited to,gamma-glycidoxypropyltrimethoxysilane,gamma-ureidopropyltrialkoxysilane, gamma-aminopropyltriethoxysilane, andthe like. Generally the additives are added directly to either one ofPart 1 or Part 2, or both, as appropriate, before admixture withaggregate. In this manner either Part 1 or Part 2, or both, can besupplied ready for use in making foundry cores and molds.

The epoxy acrylate binder system of this invention contains an epoxyresin component (Part 1) and an acrylate component (Part 2). Theweight/weight ratio of the epoxy resin component (Part 1) to theacrylate component (Part 2) can range from about 3:1 to about 1:2. In apreferred embodiment, the weight/weight ratio of the epoxy resincomponent (Part 1) to the acrylate component (Part 2) ranges from about2:1 to about 1:1.

Various types of aggregate and amounts of binder can be used to preparefoundry mixes by methods well known in the art. The aggregate materialscommonly used in the foundry industry include silica sand, lake sand,bank sand, construction aggregate, quartz, chromite sand, zircon sand,or the like. Reclaimed sand may also be used.

Sand sold under the product designation F-5574, available from BadgerMining Corporation, Berlin, Wis., is useful in making cores and molds ofthe embodiments of the present invention. Likewise, sand sold under theproduct designation Wedron 530, available from Wedron Silica, a divisionof Fairmount Minerals, Wedron, Ill., is also useful. Incast 55 silicasand, available from Unimin Corp., Oregon, Ill., may also be used. Sandsold under the product designation Nugent 480, available from NugentSand Company, Muskegon, Mich., may also be used. As known in the art,the sand type, grain size and distribution will affect the strengthdevelopment of the bound aggregate.

In ordinary sand type foundry applications, the amount of binder isgenerally no greater than about 5% by weight and frequently within therange of about 0.5% to about 4% by weight based upon the weight of theaggregate. It has been found that the epoxy acrylate binder made inaccordance with the present invention is effective when present in anamount from about 0.5% to about 2% by weight based on the total weightof the foundry mix. It should be noted that, generally, high binderlevels cause gas related defects in castings as well as result in highemission of volatile organic compounds.

The foundry mix is molded into the desired shape by ramming, blowing, orother known foundry core and mold making methods into a suitable corebox or pattern. The shape is then cured by the cold-box process, usingvaporous sulfur dioxide as the curing agent. The shaped article ispreferably exposed to effective catalytic amounts of 100 percentvaporous sulfur dioxide, although minor amounts of a carrier gas such asnitrogen may also be used. The exposure time of the sand mix to the gasis typically from 0.5 to 3 seconds. The flow rate of the sulfur dioxidegas is dependent, of course, on the size of the shaped foundry mix aswell as the amount of binder contained therein. Sufficient sulfurdioxide is passed through the shaped foundry mix to providesubstantially complete reaction between the epoxy resin components andthe acrylate components and to produce a cured foundry shape. The sulfurdioxide gas is injected at ambient temperature and at a pressure whichcan vary depending on the dimensions of the shape to be manufactured.The pressure must be sufficient for the gas to be dispersed uniformlythroughout the entire bulk of the foundry shape and to escape to theoutside of the mold. The cured shaped article can be purged of sulfurdioxide with an inert gas, such as nitrogen.

The following examples further illustrate the invention. They should notbe construed as in any way limiting the scope of the invention.

Test Procedure

Resins were tested for hot strength as described in the examples belowusing the following procedure. 16.08 grams of Part 1 resin and 7.92grams of Part 2 resin were coated on to 2000 grams of Wedron 530 sandusing a Hobart mixer at speed 2 for 90 seconds. The resulting resincoated sand was used to make 1⅛″ d.×2″ ht. cylinder test specimens in adie, equipped to make three test specimens at a time. The resin-coatedsand was blown into the die and cured by gassing with SO₂ for threeseconds, followed by 15 seconds purge with nitrogen. The test specimenswere stored in a desiccator for 2 hours prior to testing in a DietertNo. 785 Thermolab Dilatometer with the furnace equilibrated at 1800° F.A test specimen was placed in the dilatometer and subjected to a 50 psicompressive load. These conditions simulate the core behavior under theferrostatic pressure of molten metal. The time it took for a testspecimen to collapse was then measured. The time taken for the testspecimen to collapse is indicative of its thermostability. Resins givinghigher collapse times are thermally stable and will improve hot strengthand vice versa. Six test specimens were tested in each instance and anaverage collapse time of those six results is reported.

In the examples below, higher collapse times indicate higher hotstrength under core-making conditions. The collapse times are directlyproportional to hot strength, so a shorter collapse time is indicativeof poor hot strength.

EXAMPLE 1

Part 1 was prepared by mixing Bisphenol F type epoxy resin (45.6 grams),3.6 epoxy novolac resin (25 grams), butyl ester of tall oil fatty acid(0.9 grams) and cumene hydroperoxide (28.5 grams). Part 2 was preparedby mixing Bisphenol A type epoxy resin (19.85 grams), trimethylolpropanetriacrylate (45.16 grams), hexanediol diacrylate (34 grams), butylatedcresol (0.09 grams) and gamma-glycidoxypropyltrimethoxysilane (0.9grams). Parts 1 and 2 were used in the test procedure above.

EXAMPLE 2

Part 1 was prepared as in Example 1. Part 2 was prepared as in Example1, except 2 grams of tri-n-butyl borate was substituted for 2 grams ofBisphenol A type epoxy resin. The amount of tri-n-butyl borate was 2% byweight based on the total weight of Part 2.

EXAMPLE 3

Part 1 was prepared as in Example 1. Part 2 was prepared as in Example1, except 6 grams of tri-n-butyl borate was substituted for 6 grams ofBisphenol A type epoxy resin. The amount of tri-n-butyl borate was 6% byweight based on the total weight of Part 2.

TABLE 1 Example No. Collapse Time, sec. 1 165 2 175 3 155

Table 1 demonstrates the improvements in hot strength properties asshown by a 6% increase in collapse time using the Example 2 binder incomparison to the cylinder test specimens of Example 1, in which noborate is used. Higher collapse times indicate higher hot strength undercore-making conditions. In contrast, the collapse time using the Example3 binder decreased in comparison to the cylinder test specimens ofExample 1, which indicates that the beneficial effect in this particularsystem resulted when tri-n-butyl borate was used in an amount less thanabout 6% by weight based on the total weight of Part 2.

EXAMPLE 4

Part 1 was prepared by mixing a Bisphenol A type epoxy resin (12.5grams), Bisphenol F type epoxy resin (45.6 grams), 3.6 epoxy novolacresin (12.5 grams), butyl ester of tall oil fatty acid (0.9 grams) andcumene hydroperoxide (28.5 grams). Part 2 was prepared by mixing aphenolic urethane cold-box resin “Sigma Cure 705”—a product of HAInternational, Westmont, Ill. (19.85 grams), trimethylolpropanetriacrylate (45.16 grams), hexanediol diacrylate (34 grams), butylatedcresol (0.09 grams) and gamma-glycidoxypropyltrimethoxysilane (0.9grams). Parts 1 and 2 were used in the test procedure above.

EXAMPLE 5

Part 1 was prepared as in Example 4. Part 2 was prepared as in Example4, except 2 grams of tri-n-butyl borate was substituted for 2 grams ofSigma Cure 705 resin. The amount of tri-n-butyl borate was 2% by weightbased on the total weight of Part 2.

EXAMPLE 6

Part 1 was prepared as in Example 4. Part 2 was prepared as in Example4, except 4 grams of tri-n-butyl borate was substituted for 4 grams ofSigma Cure 705 resin. The amount of tri-n-butyl borate was 4% by weightbased on the total weight of Part 2.

TABLE 2 Example No. Collapse Time, sec. 4 154 5 186 6 181

Table 2 demonstrates the improvements in hot strength properties asshown by increased collapse times using the Example 5 and 6 binders, of21% and 18%, respectively, in comparison to the cylinder test specimensof Example 4, in which no borate is used. Higher collapse times indicatehigher hot strength under core-making conditions.

EXAMPLE 7

The resin from Example 1 and the resin from Example 5 were comparedusing a standard casting erosion test: “Test Casting Evaluation ofChemical Binder Systems,” Tordoff et al., AFS Transactions, 1980, Vol.74, p. 152-153, developed by British Steel Casting Research Association,which is hereby incorporated by reference. In this test, molten iron atapproximately 2580° F. was poured into a 1 inch diameter, 16 inch highsprue. The molten metal then impinges on a molded sand surface inclinedat 60 degrees. The metal was poured until the bottom cavity, which holdsabout 60 pounds of metal, the wedge shaped section, and the sprue werefilled with molten metal. The assembly was allowed to cool and the wedgeshaped section was removed and the amount of erosion was measured. Acasting defect due to erosion appears as a protuberance on the wedgeshaped section. The area of the protuberance was measured to determinethe extent of the erosion. This test was run on, in duplicate, usingmolds made with the resin of Example 1 and the resin from Example 5 withthe following results. The sand mix used was Incast 55 silica sand, 1.2%total resin and a Part 1/Part 2 ratio of 2/1.

TABLE 3 Metal Temp. Erosion Area Average Erosion Resin System (° F.)(sq. in.) (sq. in.) Example 1-A 2584 3.52 Example 1-B 2593 3.67 3.60Example 5-A 2593 1.28 Example 5-B 2565 0.4 0.84

This test showed that the resin system in Example 5, containing theborate compound, had 77% less erosion than the resin system in Example1.

EXAMPLE 8

The resin system in Examples 1 and 5 were also tested in a foundrysituation on a casting where erosion always occurred. Twenty four coreswere made with each system, placed in molds, and then poured with molteniron at 2700° F. After cooling, the castings were removed from the moldsand examined for erosion. They were rated either acceptable or scrap.Results are shown in Table 4.

TABLE 4 Resin System % Acceptable % Scrap Example 1 8.3 91.7 Example 557 43

The improved system of Example 5 reduced erosion in the castingssubstantially. Furthermore, it was found that erosion on the Example 5system could be eliminated by brushing a small area with a refractorycoating, while in contrast the entire core had to be coated with theExample 1 system.

EXAMPLE 9

If a resin system were prepared by substituting triethyl borate fortri-n-butyl borate in either Example 5 or 6, it is expected that alonger collapse time would result in comparison to the cylinder testspecimens of Example 4, in which no borate is used. The amount oftriethyl borate would be 2-4% by weight based on the total weight ofPart 2.

EXAMPLE 10

If a resin system were prepared by substituting tri-n-propyl borate fortri-n-butyl borate in either Example 5 or 6, it is expected that alonger collapse time would result in comparison to the cylinder testspecimens of Example 4, in which no borate is used. The amount oftri-n-propyl borate would be 2-4% by weight based on the total weight ofPart 2.

EXAMPLE 11

If a resin system were prepared by substituting triisopropyl borate fortri-n-butyl borate in either Example 5 or 6, it is expected that alonger collapse time would result in comparison to the cylinder testspecimens of Example 4, in which no borate is used. The amount oftriisopropyl borate would be 2-4% by weight based on the total weight ofPart 2.

EXAMPLE 12

If a resin system were prepared by substituting triisobutyl borate fortri-n-butyl borate in either Example 5 or 6, it is expected that alonger collapse time would result in comparison to the cylinder testspecimens of Example 4, in which no borate is used. The amount oftriisobutyl borate would be 2-4% by weight based on the total weight ofPart 2.

EXAMPLE 13

If a resin system were prepared by substituting tri-sec-butyl borate fortri-n-butyl borate in either Example 5 or 6, it is expected that alonger collapse time would result in comparison to the cylinder testspecimens of Example 4, in which no borate is used. The amount oftri-sec-butyl borate would be 2-4% by weight based on the total weightof Part 2.

EXAMPLE 14

If a resin system were prepared by substituting tri-tert-butyl boratefor tri-n-butyl borate in either Example 5 or 6, it is expected that alonger collapse time would result in comparison to the cylinder testspecimens of Example 4, in which no borate is used. The amount oftri-tert-butyl borate would be 2-4% by weight based on the total weightof Part 2.

EXAMPLE 15

If a resin system were prepared by substituting tri-n-octyl borate fortri-n-butyl borate in either Example 5 or 6, it is expected that alonger collapse time would result in comparison to the cylinder testspecimens of Example 4, in which no borate is used. The amount oftri-n-octyl borate would be 2-4% by weight based on the total weight ofPart 2.

EXAMPLE 16

If a resin system were prepared by using any of 1% by weight, 1.5% byweight, 5% by weight, or 5.8% by weight of tri-n-butyl borate in Example5 (all substituting for a corresponding amount of Sigma Cure 705 resin),it is expected that a longer collapse time would result in comparison tothe cylinder test specimens of Example 4, in which no borate is used.The amount of tri-n-butyl borate would be 1% by weight, 1.5% by weight,5% by weight, and 5.8% by weight, respectively, based on the totalweight of Part 2.

Although the above examples are intended to be representative of theinvention, they are not intended to limit the scope of the appendedclaims. It will be apparent to those skilled in the art thatmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

1. A sulfur dioxide-curable binder composition comprising: an epoxyresin component including at least one epoxy resin and a free radicalinitiator; and an acrylate component including at least one acrylate anda boric acid ester, wherein the boric acid ester is present in an amountof about 1% to less than about 6% by weight based on the weight of theacrylate component.
 2. The binder of claim 1 wherein the boric acidester is a trialkyl borate.
 3. The binder of claim 2 wherein thetrialkyl borate is a tri(C₂-C₈)alkyl borate.
 4. The binder of claim 3wherein the tri(C₂-C₈)alkyl borate is selected from the group consistingof triethyl borate, tri-n-propyl borate, tri-isopropyl borate,tri-n-butyl borate, tri-isobutyl borate, tri-sec-butyl borate,tri-tert-butyl borate, and tri-n-octyl borate.
 5. The binder of claim 1wherein the boric acid ester is present in an amount of about 2% toabout 4% by weight based on the weight of the acrylate component.
 6. Thebinder of claim 2 wherein the trialkyl borate is present in an amount ofabout 2% to about 4% by weight based on the weight of the acrylatecomponent.
 7. The binder of claim 6 wherein the weight/weight ratio ofthe epoxy resin component to the acrylate component is from about 2:1 toabout 1:1.
 8. The binder of claim 1 wherein the acrylate componentfurther includes a phenolic resin.
 9. A sulfur dioxide-curable bindercomposition comprising: an epoxy resin component including at least oneepoxy resin and a free radical initiator; and an acrylate componentincluding at least one acrylate and tri-n-butyl borate, whereintri-n-butyl borate is present in an amount of about 1% to less thanabout 6% by weight based on the weight of the acrylate component. 10.The binder of claim 9 wherein tri-n-butyl borate is present in an amountof about 2% to about 4% by weight based on the weight of the acrylatecomponent.
 11. The binder of claim 10 wherein the weight/weight ratio ofthe epoxy resin component to the acrylate component is about 2:1. 12.The binder of claim 11 wherein the epoxy resin component comprises anepoxy resin selected from the group consisting of bisphenol F, bisphenolA, epoxy novolac, and mixtures thereof.
 13. The binder of claim 12wherein the acrylate component comprises an acrylate monomer.
 14. Thebinder of claim 13 wherein the acrylate monomer is selected from thegroup consisting of trimethylolpropane triacrylate, hexanedioldiacrylate, and mixtures thereof.
 15. The binder of claim 14 wherein theacrylate component further includes a phenolic urethane resin.
 16. Asulfur dioxide-curable foundry mix comprising: aggregate; and a binderincluding an epoxy resin component and an acrylate component, the epoxyresin component including at least one epoxy resin and a free radicalinitiator, and the acrylate component including at least one acrylateand a boric acid ester, wherein the boric acid ester is present in anamount of about 1% to less than about 6% by weight based on the weightof the acrylate component; and the binder being present in an amountfrom about 0.5% to about 2% based on the total weight of the foundrymix.
 17. The foundry mix of claim 16 wherein the boric acid ester is atrialkyl borate.
 18. The foundry mix of claim 17 wherein the trialkylborate is a tri(C₂-C₈)alkyl borate.
 19. The foundry mix of claim 18wherein the tri(C₂-C₈)alkyl borate is selected from the group consistingof triethyl borate, tri-n-propyl borate, tri-isopropyl borate,tri-n-butyl borate, tri-isobutyl borate, tri-sec-butyl borate,tri-tert-butyl borate, and tri-n-octyl borate.
 20. The foundry mix ofclaim 18 wherein the tri(C₂-C₈)alkyl borate is tri-n-butyl borate. 21.The foundry mix of claim 16 wherein the boric acid ester is present inan amount of about 2% to about 4% by weight based on the weight of theacrylate component.
 22. The foundry mix of claim 20 wherein tri-n-butylborate is present in an amount of about 2% to about 4% by weight basedon the weight of the acrylate component.
 23. The foundry mix of claim 22wherein the weight/weight ratio of the epoxy resin component to theacrylate component is about 2:1.
 24. The foundry mix of claim 23 whereinthe epoxy resin component comprises an epoxy resin selected from thegroup consisting of bisphenol F, bisphenol A, epoxy novolac, andmixtures thereof.
 25. The foundry mix of claim 24 wherein the acrylatecomponent comprises an acrylate monomer.
 26. The foundry mix of claim 25wherein the acrylate monomer is selected from the group consisting oftrimethylolpropane triacrylate, hexanediol diacrylate, and mixturesthereof.
 27. The foundry mix of claim 16 wherein the acrylate componentfurther includes a phenolic resin.
 28. A method of making a foundryshape, comprising the steps of: (a) preparing a foundry mix by admixingaggregate and a binder comprising an epoxy resin component including atleast one epoxy resin and an effective amount of a peroxide; and anacrylate component including at least one acrylate and a boric acidester, wherein the boric acid ester is present in an amount of about 1%to less than about 6% by weight based on the weight of the acrylatecomponent; and wherein the binder is present in an amount from about0.5% to about 2% based on the total weight of the foundry mix; (b)shaping the foundry mix to a desired configuration to provide a shapedfoundry mix; and (c) curing the shaped foundry mix with gaseous sulfurdioxide to provide a foundry shape.
 29. The method of claim 28 whereinthe boric acid ester is a trialkyl borate.
 30. The method of claim 29wherein the trialkyl borate is a tri(C₂-C₈)alkyl borate.
 31. The methodof claim 30 wherein the tri(C₂-C₈)alkyl borate is selected from thegroup consisting of triethyl borate, tri-n-propyl borate, tri-isopropylborate, tri-n-butyl borate, tri-isobutyl borate, tri-sec-butyl borate,tri-tert-butyl borate, and tri-n-octyl borate.
 32. The method of claim30 wherein the tri(C₂-C₈)alkyl borate is tri-n-butyl borate.
 33. Themethod of claim 32 wherein tri-n-butyl borate is present in an amount ofabout 2% to about 4% by weight based on the weight of the acrylatecomponent.
 34. The method of claim 33 wherein the weight/weight ratio ofthe epoxy resin component to the acrylate component is about 2:1. 35.The method of claim 34 wherein the epoxy resin component comprises anepoxy resin selected from the group consisting of bisphenol F, bisphenolA, epoxy novolac, and mixtures thereof.
 36. The method of claim 35wherein the acrylate component comprises an acrylate monomer.
 37. Themethod of claim 36 wherein the acrylate monomer is selected from thegroup consisting of trimethylolpropane triacrylate, hexanedioldiacrylate, and mixtures thereof.
 38. The method of claim 28 wherein theacrylate component further includes a phenolic resin.